Thermal Machine: Solving for Q23 to Complete the Otto Cycle

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SUMMARY

The discussion focuses on solving for Q23 in the context of the Otto Cycle using thermodynamic equations. The participants detail the relationships between pressure and volume during adiabatic and isochoric processes, specifically using the equations P1V1^γ = P2V2^γ and T1V1^{1-γ} = T2V2^{1-γ}. The values provided include P2 at 18.4 x 10^5 Pa and T2 at 429.32 K. The main challenge identified is the inability to find values for P3, P4, T3, and T4, which can be resolved by expressing these variables in terms of Q23 to complete the cycle.

PREREQUISITES
  • Understanding of the Otto Cycle thermodynamic processes
  • Familiarity with adiabatic and isochoric equations
  • Knowledge of the specific heat ratio (γ)
  • Proficiency in manipulating thermodynamic equations
NEXT STEPS
  • Study the derivation and application of the Otto Cycle equations
  • Learn how to express thermodynamic variables in terms of heat transfer
  • Explore the implications of the specific heat ratio (γ) in thermodynamic cycles
  • Investigate numerical methods for solving thermodynamic equations
USEFUL FOR

This discussion is beneficial for mechanical engineers, thermodynamics students, and professionals involved in engine design and analysis, particularly those focusing on the Otto Cycle and heat transfer calculations.

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Homework Statement
Consider an Otto Cycle:
1-->2 (adiabatic)
2-->3 (isochoric)
3-->4 (adiabatic)
4-->1 (isochoric)

Knowing that:

P1 = 10^5 Pa
V1= 0,8 m^3
T1 = 290K
V3= 0,1m^3
cv= 0,171 Kcal/kg . K
Gas mass = 1 kg
gamma (coefficient of adiabatic expansion) = 1,4
V1=V4
V2=V3
Q23 = heat received
Q41 = heat expelled

Find T2,T3,T4 and P2,P3,P4
Relevant Equations
pv/t = constant
p(v)^gamma= constant
t v^(1-gamma) = constant
Q = m. cv . (T'-T)
1-->2 (adiabatic)

$$P_1V_1^γ=P_2V_2^γ$$

$$P_2=18,4.10^5Pa$$

$$T_1V_1^{1-\gamma}=T_2V_2^{1-\gamma}$$

$$T_2=429,32K$$

2-->3 (isochoric)

$$\frac{P_2}{T_2}=\frac{P_3}{T_3}$$

$$\frac{18,4.10^5}{429,32}=\frac{P_3}{T_3}$$

3--> 4 (adiabatic)

$$P_3V_3^{\gamma}=P_4V_4^{\gamma}$$

$$T_3V_3^{\gamma-1}=T_4V_4^{\gamma-1}$$

4--> 1 (isochoric)

$$\frac{P_1}{T_1}=\frac{P_4}{T_4}$$

From here, I can no longer find the values of P3, P4, T3, T4, as it is as if each equation is an association of the other. So I was wondering if there is a way to resolve this issue, because for me, I believe that data is missing.
 
Physics news on Phys.org
Data is not missing. Express everything for points 3 and 4 in terms of Q23. Solve for the value of Q23 that closes the loop at point 1.
 

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